Chung Law and Yiguang Ju have carried out fundamental research on hydrogen and dimethyl ether combustion to pave the way for use of alternative fuels in the transportation sector. Law’s group also addresses the safety issues in handling and storage of hydrogen gas by analyzing the explosion hazards associated with the sudden release of a high pressure hydrogen jet into air. This year, research was conducted on three projects related to safety and utilization aspects of combustion.

 


Initiation of explosions

An important aspect of the hydrogen economy is the safety associated with storage and handling of a light and highly reactive gas. This year Law’s group has continued its investigation of the initiation of accidental fires and explosions upon the puncture of a high-pressure hydrogen storage tank. The evolution of the gaseous jet issuing from the puncture was computationally simulated, including the associated shock trains that could potentially heat up the gas to initiate the reaction and hence explosion.

 


Flame front instability

In the early years of the grant, Law’s team determined the conditions for hydrogen ignition and hydrogen flame propagation. They found that the flame surface at higher pressures becomes unstable, leading to cellular pulsations. The effect was found to increase the flame speed and burning rate of fuel, a beneficial aspect of hydrogen use in ICE’s promoting the power of the engine.

However, hydrogen gas can sometimes be too easily ignited under supercharged conditions, creating undesirable high pressure shock waves in a phenomenon known as engine knock. Law and his group proposed a new strategy to limit knock while maintaining the desirable aspects of hydrogen combustion. They showed that dilution of the hydrogen gas with a heavier fuel such propane may eliminate the propensity of the flame to be destabilized by reducing the flame sensitivity. This finding implies that use of hydrogen/propane mixtures could reduce the need for supercharging required in an engine, reduce the tendencies for the detrimental events of knock and pre-ignition, and lower the potential for explosion of hydrogen in storage.

This year, the transition of a spark-ignited outwardly propagating flame front from a smooth surface to a wrinkled one was experimentally studied in high-pressure environments simulating those within internal combustion engines, with the anticipation that the increases in the flame surface area would increase the propagation rate that could eventually lead to self-turbulization of the flame. The experimental results on the transition state agree well with theoretical predictions (Figure 5).

Figure 5. Images of expanding hydrogen and propane flames. Rich hydrogen and lean propane flames remain smooth during flame propagation, while lean hydrogen and rich propane flames become wrinkled and hence could self turbulize.

 


Collaboration with Ford on engine simulations

Collaboration has been initiated with researchers at Ford (James Yi and Claudia Iyer) to improve the simulation capability of their engine codes. The improvement has been conducted along two directions: facilitation of the engine code itself, and the reduction of the extremely large detailed chemical reaction mechanisms of fuels oxidation to sizes that can be accommodated in engine codes. It is noted that our initial contributions have already resulted in an increase in the computation speed by 33%, without loss of accuracy. Figure 6 shows that there is no detectable difference in the predicted pressure rise during combustion in the engine cylinder when using the revised computer code (ckwyp) that we supplied.

Figure 6. Comparison between the computed pressure rise during engine combustion using the previous and improved computer codes (ckwyp), showing there is no loss in accuracy while gaining 33% speedup in the computation.